Described herein are ink jet inks that are comprised of wax backbones containing at least one functionalized group, and methods of forming an image with such inks.
The volume of digital color printing is expected to experience significant growth in the coming years. The color images provided by ink jet printing inks are overwhelmingly preferred in panel studies over other digital imaging systems. There is also a strong case to be made that the total cost of ownership of an ink jet printer will ultimately be cheaper than similar volume electrophotography units.
Ink jetting devices are known in the art, and thus extensive description of such devices is not required herein. As described in U.S. Pat. No. 6,547,380, incorporated herein by reference, ink jet printing systems are generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium. There are three types of drop-on-demand ink jet systems. One type of drop-on-demand system is a piezoelectric device that has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as acoustic ink printing. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands.
In a typical design of a piezoelectric ink jet device, the image is applied by jetting appropriately colored inks during four to six rotations (incremental movements) of a substrate (e.g., an intermediate transfer member surface) with respect to the ink jetting head, i.e., there is a small translation of the printhead with respect to the substrate in between each rotation. This approach simplifies the printhead design, and the small movements ensure good droplet registration.
In certain ink jet devices, including piezoelectric devices, it is desirable to employ transfuse, i.e., a transfer and fusing step, in forming the image. Transfuse plays an important role in piezoelectric ink jet printers by enabling a high quality image to be built up on a rapidly rotating transfer member. This approach simplifies the printhead design, while the small movements of the head ensures good droplet registration. Transfuse typically involves jetting the ink from the ink jet head onto an intermediate member such as a belt or drum, i.e., a transfuse member. This allows the image to be rapidly built onto the transfuse member and then subsequently transferred and fused to an image receiving substrate.
Hot melt inks typically used with ink jet printers of the aforementioned type utilize a wax based ink vehicle, e.g., a crystalline wax. Such solid ink jet inks provide vivid color images. These crystalline wax inks are jetted at temperatures at which they are liquids, and then are cooled to solidify on the intermediate transfuse member before being transferred to an image receiving substrate such as paper. Transfuse spreads the image droplet, providing a richer color and lower pile height. The low flow of the solid ink also prevents show through on the paper.
In particular, the crystalline wax inks are jetted onto a transfuse member, for example, an aluminum drum, at temperatures of approximately 130-140° C. The wax based inks are heated to such high temperatures to decrease their viscosity (i.e., to change the inks from a solid state at room temperature to liquid at jetting temperature) for efficient and proper jetting onto the transfuse member. The transfuse member is heated to approximately 60° C., so that the wax will cool sufficiently to solidify or crystallize. As the transfuse member rolls over the recording medium, e.g., paper, the image comprised of wax based ink is pressed into the paper.
However, the use of crystalline waxes alone has shortcomings. For example, the crystalline waxes tend to be brittle so as not to provide robust images, and are also easily scratched. This is because wax based inks generally crystallize at temperatures greater than room temperature and therefore, the wax based ink that has been transferred to the recording medium is essentially as hard as it will get. The fragile images cause customer dissatisfaction, and in some markets prevents sales penetration.
Xerox Corporation discovered that curing ultraviolet (UV) photosensitive ink jet inks by photoinitiation of the reactive inks can provide tough, permanent images on an image receiving substrate. See, for example, U.S. Pat. Nos. 6,561,640 and 6,536,889, each incorporated herein by reference in its entirety. These patents describe processes of forming ink jetted images using UV curable inks. Co-pending Application No. 11/034,850 entitled “Low Level Cure Transfuse Assist for Printing with Radiation Curable Ink,” incorporated herein by reference in its entirety, describes ink compositions for use in such processes. Co-pending Application No. 11/034,856 entitled “Ink Jet Ink Curable Via Different Polymerization Routes,” incorporated herein by reference in its entirety, describes ink compositions in which the ink vehicle comprises a mixture of at least one cationically curable component and at least one radically curable component.